Your fact is that a (singular) Japanese manufacturer made an electric car which was ~popular. Even if it was the most popular selling
electric car, it's dwarfed by sales of every other type of car (on every continent). Despite being on sale for ~8 years in Europe, it's still a novelty seeing one on the road. The Leaf wasn't the kick up the arse that other manufacturers needed, the Tesla 3 arguably was.
This is in spite of Europe being a massive consumer of Japanese cars in general(Nissan & Toyota in particular).
Assuming Tesla 3 doesn't get down to sub €35k price in the next year, Hynudai Kona seems like it will be the best selling EV in Europe in 2019 (provided the end dealers don't mess it up)
Some other Japanese manufacturers:
Toyota, Honda, Daihatsu, Suzuki, Mazda, Mitsubishi, Subaru, Isuzu
Barring Toyota who at least made some effort with the Prius. What have the rest of those industry players done for EV adoption/advancement? Nothing. Some (even in 2019) still haven't made inroads into EV.